2.1 Field of the Invention
The present invention relates to light-emitting materials and devices constructed using such materials. More specifically, the present invention relates to organic, electroluminescent materials and associated devices. The present invention has applications in the areas of materials science, organic chemistry, and electronics.
2.2 The Related Art
Makers of electronic devices that produce visual information, such as computers, are working intensely to develop display devices that provide brighter, sharper pictures at lower manufacturing cost and less weight. The drive to lighter, cheaper, better displays has lead to the development of flat-panel displays ("FPDs") that are commonly used in laptop computers and include a growing share of the desktop computer display market. FPDs are almost exclusively liquid crystal displays ("LCDs"). However, LCD technology has shortcomings, including weak brightness and large power requirements.
One alternative to LCDs are electroluminescent ("EL") displays. EL displays use the luminescense of a solid film that is produced when a voltage is applied to the solid film. Referring to FIG. 1, which illustrates the process generally, the electroluminescent material ("EML") is placed between a cathode and an anode. The application of an electric potential (typically 100 MV/m) injects holes into the highest occupied molecular orbital ("HOMO") or valence band ("VB") of the EML from the anode, and electrons are injected into the lowest unoccupied molecular orbital ("LUMO") of the EML or conduction band ("CB"). The recombination of the electrons and holes in the EML causes the emission of light from EML.
To facilitate the production of holes and electrons, a hole transport layer ("HTL") and/or electron transport layer ("ETL") are provided to increase the efficiency of hole (electron) injection and recombination. This has lead to the design of EL displays having the general structure shown in FIG. 2 at 200. There, an electrode 202 is coupled with an electron transport layer 204. ETL 204 is coupled with electroluminescent layer 206, which, in turn, is coupled with hole transport layer 208. HTL 208 is coupled with electrode 210. Electrodes 202 and 210 are connected by contacts 212 and 214 that are each coupled to a source 216.
Presently, EL displays are fabricated using either inorganic materials, such as manganese (Mn)-doped zinc sulfide (ZnS), or organic materials such as polyphenylene vinylene ("PPV") and its derivatives. However, no satisfactory EL material has been developed for widespread applications. Although inorganic EL displays can provide high performance and durability, they suffer from large power requirements and expensive, low-throughput fabrication processes. Thus, inorganic EL displays have been relegated largely to niche applications, such as military and medical applications. Organic EL displays, on the other hand, can be fabricated more cheaply and simply than inorganic EL displays, but suffer from relatively poor performance. Thus, a need remains to provide an EL display having a cost/performance profile that is suitable for the general marketplace. Such a device will require materials that are relatively inexpensive and simple to prepare compared to inorganic EL displays while providing comparable performance characteristics. The present invention meets these and other needs.